Long range bullets are designed to provide a flat trajectory and stable flight over long distances. To achieve a flat trajectory the nose, bearing surface and boat tail needs to be aerodynamically optimized.
Typically long range bullets have a spitzer or small meplat point, boat tail and a relatively long curved/ogive nose and a smooth body. The bullets normally have an ogive part (i), cylinder part (ii) (bore bearing part) and the frustum part (iii) of the boat tail, see FIG. 8. The surface of the cylinder part bears against the bore of the barrel when fired and also fits in the neck of a cartridge/case. Long range boat tail bullets are typically used on targets at 200 m and beyond. Flat base bullets are used for high accuracy over shorter distances, normally for distances less than 300 m.
The inventor is aware of, from an internal ballistics point of view, the requirement for a good seal between the bullet and the bore of the barrel and engagement with the rifling of the barrel. However, this requirement causes friction and drag in the barrel as the bullet accelerates through the bore of the barrel, which, if excessive, causes high chamber pressures. The chamber pressure is at its peak shortly after ignition of the propellant. If the peak pressure is too high, it can cause a catastrophic explosion. There is a need for mono metal bullets which provide the required seal and rifling engagement with the minimum required in-barrel friction enabling controlled chamber pressures and increased muzzle velocity. This can be accomplished by designing a mono metal bullet with less bearing/contact surface against the inside of the barrel such as can be achieved by a set of circular rings provided about the bearing surface of a bullet. The rings or grooves are typically used as cannelure rings such as the rings described in PCT/ZA2012/000093. These rings or grooves are dimensioned to the bore diameter 1 of a barrel, while the cylinder diameter is dimensioned to the groove diameter 2. See FIGS. 8 and 9. The groove depth is shown by 3. The main problem with such rings or grooves is that they increase the aerodynamic drag and therefore lower the ballistic coefficient/aerodynamic performance of a bullet. The groove shape on the bearing surface of mono metal bullets is traditionally not aerodynamically optimized. The main purpose of grooves is to control in-barrel friction and pressure build up whilst ignoring the detrimental aerodynamic effect during free flight of the bullet. It can be shown that the typical drag of a groove will be significantly decreased by adjusting the leading and trailing edge angles of the groove to create weak shock waves instead of strong shock waves during supersonic flight.
In addition, use of any other material harder than pure copper such as brass, can also cause over pressure in the chamber when fired and it is a further object to be able to reduce the chamber pressure for all such bullets without the need to use grooves with detrimental aerodynamic effects.
It is an object of the invention to provide an extended range mono metal bullet with controlled friction within the barrel whilst maintaining a good seal with the groove diameter and without the aerodynamic sacrifice of grooves on the bullet.